The invention relates to an automatic soldering method and the apparatus thereof and more particularly relates to a method for arranging an elongated molten solder storing tank laterally of a base board transporting direction in a manner as inclined with respect to the base board transporting direction in a horizontal plane while transporting a base board in a manner that a horizontal position of the base board is progressively moved up as the base board is transported and further in a manner that the base board is inclined in a vertical plane intersecting the base board transporting direction such that a distance between a lower side of the base board and a top of an elongated molten solder jetting nozzle provided in the solder storing tank is constant all through the length of the nozzle as the base board is transported part over the nozzle, to thereby secure a same soldering condition between the points of the base board to be soldered and the molten solder jetted up from the nozzle all through the length of the nozzle.
Another aspect of the invention relates to a method and the apparatus thereof for transporting a carrier carrying the base board to be soldered from a base board entrance side to a soldered base board exit side of a base board transporting path and then feeding back the carrier from the soldered base board exit side to the base board entrance side so that the carrier may carry a new base board to be soldered again.
A conventional automatic soldering method and the apparatus is shown in FIGS. 12 and 13, wherein a base board 1 having electronic elements mounted thereon is soldered with the molten solder 3 jetted up from an elongated opened nozzle 2 by the action of a molten solder pressing device while the base board is transported over the nozzle arranged laterally of a base board transporting direction with the right angles.
According to the conventional method and apparatus, when a lower side 1c of the base board 1 is moved past the molten solder 3 jetting up from the nozzle 2, that is, when the soldering process is ended, the molten solder 3 will progressively flow from one end 1a toward a center 1b on the lower side 1c of the base board 1 while the molten solder is separating one after another at the soldering points of the base board. In this case, it is unavoidable that the flow of molten solder will result in the phenomena such as bridges, icicles, drops or dews formed at the center 1b of the width of the base board 1. Such defective soldering places 5 have to be confirmed by inspection and have to be amended by means of a soldering iron. Such inspection and amendment operations will increase the soldering processes and further decrease the operation efficiency. Moreover the failure of defection confirmation and the incomplete amendment will inevitably lower the quality of products.
More precisely, the base board 1 is transported while one end 1a is held, and is liable to be downwardly bent due to its own weight and the weight of the electronic parts mounted on the base board. Such downward bend will be further encouraged as the base board 1 is preheated by a heater and further heated by the molten solder at the time of soldering process. It is therefore apparent that the center part 1b of the base board 1 will be lowest and the separation of solder will be terminated at the center 1b of the base board 1.
As particularly shown in FIG. 12, the base board 1 has many points 4 provided on the lower side 1c thereof which are required to be soldered. Each of the spaces 6 between the soldering points 4 arranged laterally of the base board is very small due to the increased density of electronic parts mounted on the base board. The smallest spaces may be about 0.2 mm and so many. Therefore if the molten solder 3 comes together to one point when the base board 1 is transported past the molten solder jetting nozzle, the defective soldering phenomena will be caused such as the bridges, icicles, etc., as mentioned hereinbefore. Especially the phenomenon of bridges may be often caused in case of a base board having a higher density of electronic parts mounted at the center part 1b of the base board 1. Namely the adjacent points 4 to be soldered are bridged with the solder.
Further in case of base board 1 having one point 4 provided at the center part 1b thereof which is to be soldered, a phenomenon of icicle, drop or dew may be caused at the point because the molten solder 3 flows together a the point.
Japanese patent application made public 59-997 and Japanese patent application laid open 59-15668 disclose a method for arranging elongated nozzles 2 in a manner as inclined in a horizontal plane with respect to the base board transporting direction A in order to solve the defects and disadvantages of the prior art as mentioned above. Especially these patent applications stress a feature that the base board 1 is inclined so as to be progressively opened with respect to the plane of molten solder jetted up from the nozzles 2 as the base board is transported. It is observed that the prior art is designed to terminate the soldering process at the one end 1a of the base board 1 by simply inclining the nozzles 2 with respect to the base board transporting direction in the horizontal plane. In fact, it is admitted that the feature of the prior art will attain an effect for more or less decreasing the defective soldering results such as the soldering phenomena 5 as shown in FIG. 12. However in view of the fact that the base board 1 is progressively moved up as the base board is transported, the vertical distance between the base board 1 and the nozzles 2 is progressively higher all through the length of the nozzles 2. More precisely a period of time is progressively shorter in which the molten solder 3 contacts the lower side 1c of the base board 1 as the base board is moved past the nozzles. It is therefore apparent that the soldering condition is progressively different all through the length of the nozzles, that is, from one end to the opposite end of the base board all through the width thereof. Such variant soldering condition is far from a desired condition in which the molten solder contacts the base board for 3 seconds to attain a very best soldering effect. Namely such variant soldering condition will cause deflected soldering results.
Depending upon the arrangement of the points 4 to be soldered, it may be possible to prevent the formation of such defective soldering phenomena such as the parts 5 as shown in FIG. 12 by enlarging the inclination of the nozzles with respect to the base board transporting direction. But such enlargement of inclination is limited, and excessive inclination would make it impossible for the molten solder 3 to contact the lower side 1c of the base board 1.